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Message-ID: <116e9f61-cdf9-2eeb-51c3-a211bb1f06ca@huaweicloud.com>
Date: Wed, 7 Jun 2023 12:13:24 +0800
From: Hou Tao <houtao@...weicloud.com>
To: linux-block@...r.kernel.org, Jens Axboe <axboe@...nel.dk>
Cc: Bart Van Assche <bvanassche@....org>, Jan Kara <jack@...e.cz>,
Bagas Sanjaya <bagasdotme@...il.com>,
Chaitanya Kulkarni <kch@...dia.com>, cgroups@...r.kernel.org,
Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
Johannes Weiner <hannes@...xchg.org>,
Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
linux-doc@...r.kernel.org,
"houtao1@...wei.com" <houtao1@...wei.com>
Subject: Re: [PATCH v4] blk-ioprio: Introduce promote-to-rt policy
ping ?
On 5/23/2023 2:48 PM, Hou Tao wrote:
> ping ?
>
> On 5/8/2023 8:08 PM, Hou Tao wrote:
>> ping ?
>>
>> On 4/28/2023 3:44 PM, Hou Tao wrote:
>>> From: Hou Tao <houtao1@...wei.com>
>>>
>>> Since commit a78418e6a04c ("block: Always initialize bio IO priority on
>>> submit"), bio->bi_ioprio will never be IOPRIO_CLASS_NONE when calling
>>> blkcg_set_ioprio(), so there will be no way to promote the io-priority
>>> of one cgroup to IOPRIO_CLASS_RT, because bi_ioprio will always be
>>> greater than or equals to IOPRIO_CLASS_RT.
>>>
>>> It seems possible to call blkcg_set_ioprio() first then try to
>>> initialize bi_ioprio later in bio_set_ioprio(), but this doesn't work
>>> for bio in which bi_ioprio is already initialized (e.g., direct-io), so
>>> introduce a new promote-to-rt policy to promote the iopriority of bio to
>>> IOPRIO_CLASS_RT if the ioprio is not already RT.
>>>
>>> For none-to-rt policy, although it doesn't work now, but considering
>>> that its purpose was also to override the io-priority to RT and allowing
>>> for a smoother transition, just keep it and treat it as an alias of
>>> the promote-to-rt policy.
>>>
>>> Acked-by: Tejun Heo <tj@...nel.org>
>>> Reviewed-by: Bart Van Assche <bvanassche@....org>
>>> Reviewed-by: Chaitanya Kulkarni <kch@...dia.com>
>>> Reviewed-by: Jan Kara <jack@...e.cz>
>>> Signed-off-by: Hou Tao <houtao1@...wei.com>
>>> ---
>>> v4:
>>> * rebased on 33afd4b76393
>>> * Add Reviewed-by from Jan Kara
>>>
>>> v3: https://lore.kernel.org/linux-block/20230223135154.3749088-1-houtao@huaweicloud.com
>>> * Use 'non-RT' instead of 'no-RT' in document (from Bagas)
>>> * Remove repeated sentence in commit message
>>> * Add Reviewed-by and Acked-by tags
>>>
>>> v2: https://lore.kernel.org/linux-block/20230220135428.2632906-1-houtao@huaweicloud.com
>>>
>>> * Simplify the implementation of promote-to-rt (from Bart)
>>> * Make none-to-rt to work again by treating it as an alias of
>>> the promote-to-rt policy (from Bart & Jan)
>>> * fix the style of new content in cgroup-v2.rst (from Bagas)
>>> * set the default priority level to 4 instead of 0 for promote-to-rt
>>>
>>> v1: https://lore.kernel.org/linux-block/20230201045227.2203123-1-houtao@huaweicloud.com
>>>
>>> Documentation/admin-guide/cgroup-v2.rst | 42 ++++++++++++++-----------
>>> block/blk-ioprio.c | 23 ++++++++++++--
>>> 2 files changed, 44 insertions(+), 21 deletions(-)
>>>
>>> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
>>> index f67c0829350b..7544ce00e0cb 100644
>>> --- a/Documentation/admin-guide/cgroup-v2.rst
>>> +++ b/Documentation/admin-guide/cgroup-v2.rst
>>> @@ -2024,31 +2024,33 @@ that attribute:
>>> no-change
>>> Do not modify the I/O priority class.
>>>
>>> - none-to-rt
>>> - For requests that do not have an I/O priority class (NONE),
>>> - change the I/O priority class into RT. Do not modify
>>> - the I/O priority class of other requests.
>>> + promote-to-rt
>>> + For requests that have a non-RT I/O priority class, change it into RT.
>>> + Also change the priority level of these requests to 4. Do not modify
>>> + the I/O priority of requests that have priority class RT.
>>>
>>> restrict-to-be
>>> For requests that do not have an I/O priority class or that have I/O
>>> - priority class RT, change it into BE. Do not modify the I/O priority
>>> - class of requests that have priority class IDLE.
>>> + priority class RT, change it into BE. Also change the priority level
>>> + of these requests to 0. Do not modify the I/O priority class of
>>> + requests that have priority class IDLE.
>>>
>>> idle
>>> Change the I/O priority class of all requests into IDLE, the lowest
>>> I/O priority class.
>>>
>>> + none-to-rt
>>> + Deprecated. Just an alias for promote-to-rt.
>>> +
>>> The following numerical values are associated with the I/O priority policies:
>>>
>>> -+-------------+---+
>>> -| no-change | 0 |
>>> -+-------------+---+
>>> -| none-to-rt | 1 |
>>> -+-------------+---+
>>> -| rt-to-be | 2 |
>>> -+-------------+---+
>>> -| all-to-idle | 3 |
>>> -+-------------+---+
>>> ++----------------+---+
>>> +| no-change | 0 |
>>> ++----------------+---+
>>> +| rt-to-be | 2 |
>>> ++----------------+---+
>>> +| all-to-idle | 3 |
>>> ++----------------+---+
>>>
>>> The numerical value that corresponds to each I/O priority class is as follows:
>>>
>>> @@ -2064,9 +2066,13 @@ The numerical value that corresponds to each I/O priority class is as follows:
>>>
>>> The algorithm to set the I/O priority class for a request is as follows:
>>>
>>> -- Translate the I/O priority class policy into a number.
>>> -- Change the request I/O priority class into the maximum of the I/O priority
>>> - class policy number and the numerical I/O priority class.
>>> +- If I/O priority class policy is promote-to-rt, change the request I/O
>>> + priority class to IOPRIO_CLASS_RT and change the request I/O priority
>>> + level to 4.
>>> +- If I/O priorityt class is not promote-to-rt, translate the I/O priority
>>> + class policy into a number, then change the request I/O priority class
>>> + into the maximum of the I/O priority class policy number and the numerical
>>> + I/O priority class.
>>>
>>> PID
>>> ---
>>> diff --git a/block/blk-ioprio.c b/block/blk-ioprio.c
>>> index 055529b9b92b..4051fada01f1 100644
>>> --- a/block/blk-ioprio.c
>>> +++ b/block/blk-ioprio.c
>>> @@ -23,25 +23,28 @@
>>> /**
>>> * enum prio_policy - I/O priority class policy.
>>> * @POLICY_NO_CHANGE: (default) do not modify the I/O priority class.
>>> - * @POLICY_NONE_TO_RT: modify IOPRIO_CLASS_NONE into IOPRIO_CLASS_RT.
>>> + * @POLICY_PROMOTE_TO_RT: modify no-IOPRIO_CLASS_RT to IOPRIO_CLASS_RT.
>>> * @POLICY_RESTRICT_TO_BE: modify IOPRIO_CLASS_NONE and IOPRIO_CLASS_RT into
>>> * IOPRIO_CLASS_BE.
>>> * @POLICY_ALL_TO_IDLE: change the I/O priority class into IOPRIO_CLASS_IDLE.
>>> + * @POLICY_NONE_TO_RT: an alias for POLICY_PROMOTE_TO_RT.
>>> *
>>> * See also <linux/ioprio.h>.
>>> */
>>> enum prio_policy {
>>> POLICY_NO_CHANGE = 0,
>>> - POLICY_NONE_TO_RT = 1,
>>> + POLICY_PROMOTE_TO_RT = 1,
>>> POLICY_RESTRICT_TO_BE = 2,
>>> POLICY_ALL_TO_IDLE = 3,
>>> + POLICY_NONE_TO_RT = 4,
>>> };
>>>
>>> static const char *policy_name[] = {
>>> [POLICY_NO_CHANGE] = "no-change",
>>> - [POLICY_NONE_TO_RT] = "none-to-rt",
>>> + [POLICY_PROMOTE_TO_RT] = "promote-to-rt",
>>> [POLICY_RESTRICT_TO_BE] = "restrict-to-be",
>>> [POLICY_ALL_TO_IDLE] = "idle",
>>> + [POLICY_NONE_TO_RT] = "none-to-rt",
>>> };
>>>
>>> static struct blkcg_policy ioprio_policy;
>>> @@ -189,6 +192,20 @@ void blkcg_set_ioprio(struct bio *bio)
>>> if (!blkcg || blkcg->prio_policy == POLICY_NO_CHANGE)
>>> return;
>>>
>>> + if (blkcg->prio_policy == POLICY_PROMOTE_TO_RT ||
>>> + blkcg->prio_policy == POLICY_NONE_TO_RT) {
>>> + /*
>>> + * For RT threads, the default priority level is 4 because
>>> + * task_nice is 0. By promoting non-RT io-priority to RT-class
>>> + * and default level 4, those requests that are already
>>> + * RT-class but need a higher io-priority can use ioprio_set()
>>> + * to achieve this.
>>> + */
>>> + if (IOPRIO_PRIO_CLASS(bio->bi_ioprio) != IOPRIO_CLASS_RT)
>>> + bio->bi_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_RT, 4);
>>> + return;
>>> + }
>>> +
>>> /*
>>> * Except for IOPRIO_CLASS_NONE, higher I/O priority numbers
>>> * correspond to a lower priority. Hence, the max_t() below selects
>> .
> .
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